1. Field of the Invention
The present invention concerns circuit for switching a PIN diode, a transmission/reception diplexer, a magnetic resonance apparatus and a method for switching a PIN diode.
2. Description of the Prior Art
In magnetic resonance (MR) tomography, the different spin relaxation times T1 and T2 of different tissue types are typically used to generate an image contrast. However, for a range of tissues in the human body, the relaxation times are so short that they provide little or no signal with the typical sequences that can be realized by current technology, thus these types of tissues remain black in the MR image. Sequences known as UTE (Ultra Short Echo Time) sequences, in which 10 to 200 times less time passes between excitation and readout than in conventional magnetic resonance sequences, offer a solution to this problem. However, magnetic resonance systems normally contain a transmission/reception diplexer whose switching time limits the minimum feasible echo time to 50 to 100 μs. PIN diodes that can be switched into a radio-frequency conductive state when direct current flows through them, and into a radio-frequency blocking state via deactivation of a voltage or application of a direct voltage in the blocking direction are typically used as switching elements in a fast transmission/reception diplexer. The PIN diodes can switch power in the range of multiple kilowatts. However, the switching from the conductive state into the blocking state is temporally limited by the ultimate speed with which the charge carriers generated by the current feed into the I layer of the diode are recombined again, or drained by active discharging. The echo time has previously been adapted to the technical limits of the transmission/reception diplexer, such that the potential of UTE technology cannot be fully exploited.